Actual contact angle

The critical surface tension concept has provided a useful means of summarizing wetting behavior and allowing predictions of an interpolative nature. A schematic summary of 7 values is given in Fig. X-10 [123]. In addition, actual contact angles for various systems can be estimated since )3 in Eq. X-38 usually has a value of about 0.03-0.04. 

Fig. 1. A simplistic view of drop on a rough solid surface, demonstrating the difference between the actual contact angle (ACCA) and the apparent one (APCA).

Wolansky G, Marmur A. (1998) The actual contact angle on a heterogeneous rough surface in three dimensions. Langmuir 14 5292-5297. 

Incorporation of the measured contact angle in mercury intrusion porosimetry data is essential for an accurate determination of the pore size distribution. Both the advancing and static angle methods are suitable to carry out this measurement, leading to very similar results. For most oxidic materials and supported oxides, the contact angle is 140° and incorporation of the actual contact angle is less critical in the pore size determination. However, important deviations are observed in carbon and cement-like materials, with contact angles of > 150° and < 130°, respectively. This has been shown by comparison of the pore size distribution obtained from mercury porosimetry and N2 adsorption measurements. 

Good and Girifalco [20] and Fowkes [21], Eq. (59.7) was introduced by Owens and Wendt [22], and Eq. (59.8) was introduced by Wu [23]. Data in Table 59.3 are mostly derived via Eq. (59.7) using water and methylene iodide exceptions are noted by footnotes. Actual contact-angle data are usually, but not always, available in the references cited. As water is the ubiquitous liquid and used in many studies, a column for such data is included in Table 59.3. Where possible only quasistatic advancing contact-angle values were chosen. 

One should keep in mind that x is now not the actual contact angle, which should be zero for any finite value of k, but rather the asymptotic contact angle describing the shape of the spherical cap far from the substrate (see Fig. 22). 

Figure 7.12. Definitions of different types of contact angles (a) intrinsic contact angle, Om , (b) actual contact angle, 0ac (c) apparent contact angle, 0ap (from ref. (8)), with permission from Elsevier Science...

The difference between the actual contact angle and the macroscopic contact angle is due to the line contributions to the free energy mentioned in section 3.2.1, in particular the line tension Tivs, which influence the contact angle. Phenomenologically, the force balance (Young-Laplace) equation (3.1) for a mesoscopic droplet with a circular base of radius R (i.e., the radius of the circular wetted area) can be written as... 

Contact angles which glycerol would form on surfaces of benzophenone and blbenzyl were then predicted from the equation of state approach. Next, actual contact angle measurements with glycerol on layers of benzophenone and blbenzyl were performed. 

Contact angle measurement Specimen Actual contact angle... 

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